The speed of data communication is being pushed to ever increasing rates. The advent of Digital Subscriber Lines (DSL) now makes data communication in the megabit-per-second range possible across existing copper wire links between subscriber modems and central office modems in the public switched telephone network (PSTN).
As known to those skilled in the art, a central office provides individual subscribers with access to the PSTN. In most cases, the subscriber is linked to the central office via a twisted pair of copper wires. The central office provides an interface between the subscriber to the PSTN.
In order to facilitate DSL communication, a DSL modem is included in the link at the central office to communicate with a DSL modem used on the subscriber end of the two wire pair. DSL provides high-speed multimedia services which can operate up to approximately 400 times faster that traditional analog telephone modems.
DSL comes in several different configurations. One is the Asymmetric Digital Subscriber Line (ADSL) which provides data rates of 32 kbps to 8.192 Mbps while simultaneously providing telephone phone service. Also, Rate Adaptive Asymmetric Digital Subscriber Line (RADSL) is much like ADSL, only it allows bandwidth adjustment to fit the particular application and to accommodate the length and quality of the line. In particular, the data rate of a RADSL may be adjusted downward to accommodate a longer distance to the central office. Other configurations include High-bit-rate Digital Subscriber Line (HDSL), Symmetric Digital Subscriber Line (SDSL), and Very high-bit-rate Digital Subscriber Line (VDSL).
While DSL provides much higher rates of data communication, it is not without problems. In particular, at the higher frequencies used in DSL communication, the traditional two wire interface may not provide a reliable pathway or channel through which the data signal can travel. Often times, an interfering signal may be induced onto the two wire channel from a second two wire in close proximity. Such a signal might be from a second DSL modem that is communicating to the same central office.
Another problem may be the quality of the two wire channel itself. High frequency traffic generally experiences greater attenuation in the two wire channels. Also, interconnections that occur in the channel may degrade or loosen over a period of time, causing noise and further signal degradation.
As a result, data communication using DSL is becoming more susceptible to interference that causes disruption of the data signal. As more and more digital subscriber lines are installed, the probability of interference among two wire channels increases. Also, as the existing copper two wire network gets older, the quality of the channels will further degrade. Additionally, as DSL gains in popularity, it is likely that subscribers who are located greater distances away from central offices will desire DSL service, even though the longer distance results in greater signal attenuation.
Consequently, there is a need for a DSL transmitter which overcomes the problems of data signal interference and attenuation currently experienced.